Javascript sorting a 2D array based on condition

Question

I'm calculating the distance from points to the origin. It's a basic math calculation: Math.sqrt( Math.pow(x-0, 2) + Math.pow(y-0, 2) )

For testing, I have the points: points = [[1,3],[-2,2]]. I would like to sort it based on the smallest distance to the origin.

My code:

points.sort((a,b) => {
        const d1 = Math.sqrt( Math.pow(a[0], 2) + Math.pow(a[1], 2) ); 
        const d2 = Math.sqrt( Math.pow(b[0], 2) + Math.pow(b[1], 2) ); 
        return d1 <= d2 ? a-b : b-a; 
});

console.log(points);

The log is showing: [[1,3],[-2,2]] The 2D array is not changing. The calculation is right in the sort function. I'm not sure why it is not working.

Nina Scholz · Accepted Answer · 2020-07-15 20:35:34Z

3

You need to take the delta of the distances.

var points = [[1, 3], [-2, 2]];

points.sort((a, b) => {
  const d1 = Math.sqrt(Math.pow(a[0], 2) + Math.pow(a[1], 2));
  const d2 = Math.sqrt(Math.pow(b[0], 2) + Math.pow(b[1], 2));
  return d1 - d2;
});

console.log(points);

An even shorter approach uses Math.hypot.

var points = [[1, 3], [-2, 2]];

points.sort((a, b) => Math.hypot(...a) - Math.hypot(...b));

console.log(points);

edited Jul 15, 2020 at 20:35

answered Jul 15, 2020 at 20:31

Nina Scholz

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3 Comments

myTest532 myTest532 Over a year ago

I'm don't clearly understand how the sort() method works. Could you explain why I need to take the delta?

myTest532 myTest532 Over a year ago

I think I don't get what needs to be returned in the sort() method to sort an array

Nina Scholz Over a year ago

@myTest532myTest532, maybe you have a look here first: Array#sort. the expected result of the callback should return a value smaller than zero, if the first is smaller than the second item, zero for same items and greater than zero for all other items.

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